In the process of securing a glass windshield to a new car or truck, the manufacturer first extrudes a bead or “bed” of urethane onto the “pinch weld” extending around the perimeter of the window opening. The urethane bed bonds to the pinch weld surface. The glass windshield then is seated on the bed and bonds to it, forming a liquid-tight seal.
The urethane bed is hard and tough and not easily penetrated. It commonly has a thickness of about ¼ inch and width of about ⅓–¾ inches, widening to about 3½–4″ at the corners.
If the windshield is to be replaced, an installer severs the bed along its length, just beneath the inside surface of the glass, leaving the base portion of the bed in place. He then primes the cut surface of the bed, deposits a new bead of urethane on the primed surface and seats the replacement windshield onto the fresh bead to bond it in place.
Up to about the end of the 1980's installers used a manually operated knife to sever the urethane bed. The knife was generally L-shaped, having a narrow sharpened blade and a shank or handle equipped with hand grips. The installer would first work the point of the blade inwardly to penetrate the bed and would then reciprocate the blade with short in and out strokes while pulling the blade sideways to saw through the urethane bed along its length.
Commencing about 1990, two types of powered tools were introduced commercially, to replace the manually operated tools. These powered tools mimicked the manually operated knife in several structural and operational respects.
The first type of tool involved an L-shaped blade and shank powered by an electric motor. The blade was oscillated from side to side. The blade was pointed at its end and narrow (about ½ inch wide), to facilitate initial manual penetration. The side edge of the blade was sharpened, so that a lateral cutting action was produced.
The second type of tool involved reciprocating a blade which would extend in and out of a sleeve. The blade was actuated by an electric motor. Again, the blade was pointed and narrow (about ½ inch width), to facilitate initial penetration. The “throw” or distance advanced by the blade was short, about ½ inch.
In use, these tools were characterized by several problems. More particularly:                Cutting with them was slow. The depth and width of the cut were small, requiring a great many cuts to complete the job. Typically it would take about 15–20 minutes to cut the windshield free;        Using the prior art assemblies was laborious. The installer would have to apply a sideways pull to these tools, particularly when cutting along the horizontal legs of the bed;        It was common to crack the glass when first penetrating the bed. This could leave broken glass on the dash and elsewhere, which was undesirable;        The cuts made by the tools were shallow. One could only cut into the bed with these tools about ½ inch at a time. This meant that at the corners, where the bed width was greatest, it would take prolonged cutting to complete severing the bed. In practice, the installer would revert to using a hand knife at the corners or would break off the glass at the corners and have to later complete the cut by hand of the corner urethane with its embedded glass. In the course of hand cutting the corners, the installer would commonly press hard with his head against the windshield to assist his cutting—this was known to lead to neck injuries;        The cut surface produced by the blades of these powered tools was irregular (jagged and undulating). This was undesirable as the newly extruded bead would in part reproduce this underlying irregularity and the new windshield would then not seat flush against the bed surface. This could lead to a poor seal and subsequent leaking;        The electric motor-driven tools of the prior art were generally bulky and difficult to work with in confined space, such as the apex between the vehicle dashboard and the inside surface of the windshield;        The prior art blades were fragile and expensive—breakage was a problem; and        It was necessary to use soapy water as a coolant and lubricant for the narrow, rapidly moving blades. After the cut was complete, the cut surface needed to be carefully washed to remove soap, as it was detrimental to getting a good bond when new urethane was laid on.        